The use of hydrophobically modified anionic polymers in isotropic liquids is taught, for example, in U.S. Pat. No. 5,308,530 to Aronson et al. and in applicants copending application U.S. Ser. No. 08/591,789 to Falk et al., filed Jan. 25, 1996, now U.S. Pat. No. 5,723,434.
In these references, however, the anionic polymer required minimum levels of hydrophobic modification (i.e., ratio of hydrophile to hydrophobe below 10, preferably below 7). The greater the hydrophobic modification (more hydrophobic groups; smaller ratio of hydrophile to hydrophobe), the easier to incorporate the polymer. Such modified polymers, however, can be expensive and difficult to manufacture. Anionic polymers without hydrophobic modification on the other hand, are relatively inexpensive and readily available commercially.
Unexpectedly, applicants have found that, rather than modifying the polymer itself to make it more soluble; or rather than improving solubility using an external agent (i.e., hydrocarbon oil), by merely manipulating the surfactant composition such that sugar surfactant comprises more than 25%, preferably more than 50% of the nonionic component, it is possible to stably incorporate (solubilize) anionic polymer. Preferably, the polymer has a molecular weight under 10,000, more preferably under 8000, more preferably under 6000, more preferably about 4500 and below; more preferably about 3000 and below; and preferably the anionic polymer comprises less than about 1.5%, more preferably less than about 1% of the composition. Solubility will to some extent depend on combination of molecular weight and concentration.
Several prior art references teach compositions somewhat related but clearly different than the compositions of the invention.
EP 0,580,245 (assigned to Colgate), for example, discloses heavy duty liquid compositions containing a mixture of anionic and nonionic surfactants and including a clay softener and a detergency builder (Zeolite), wherein the use of low molecular weight polyacrylic acid (i.e., anionic polymer of MW 500 to 8000 Daltons) as a structurant is taught. Clays are said to be stabilized due to adsorption of the polymer on solids.
This reference fails to teach or suggest specific nonionic surfactants (e.g., sugar surfactants) must comprise part or all of the nonionic component of the surfactant system to obtain stability. In addition, to the extent the anionic polymer is adsorbed onto clays and is not really solubilized, the composition cannot be said to be a true isotropic composition.
EP 0,326,792 A1 (assigned to Monsanto) discloses HDL compositions containing an anionic polymer, e.g., polymeric acetal carboxylates. However, only potassium salt of the polymer is claimed to be soluble in these compositions. Furthermore, the pH of the compositions are preferred to be about 9 to 9.5 whereas the pH of the invention compositions is below 8.0. Further, these compositions require at least 5 wt.% anionic hydrotropes while the compositions of the present invention do not require hydrotropes. Finally, the reference again fails to teach or suggest the use of a specific surfactant system (i.e., sugar surfactants must comprise part or all of nonionic component) to solubilize the anionic polymers.
U.S. Pat. No. 5,332,528 to Pan et al. discloses detergent compositions containing polyacrylate and polyhydroxy fatty acids amides, a nonionic surfactant that is part of the specific surfactant system of the present invention composition. However, these compositions contain less than 12.5% surfactant. At this level, you don't need sugar and even ethoxylated alcohol would solubilize compared to the concentrated, high surfactant levels (greater than 20%) of the compositions of the invention.
WO 94/26858 (assigned to Unilever) discusses hard surface cleaning compositions containing anionic polymers and having a pH in the range of 2 to 8. These are predominantly nonionic compositions containing less than 3 wt.% anionics. The criticality of using an alkyl polysaccharide as a nonionic surfactant component is not recognized (preferred compositions, in fact, are stated to contain alcohol ethoxylates as nonionic surfactants) and total surfactants are well below the minimum 20% of the compositions of the invention.
U.S. Pat. No. 4,252,665 to Casey et al. discloses hard surface cleaning compositions containing anionic polymers. The surfactant levels of these compositions are very low (lower than 1.5 wt.%) and the pH levels are high (9 to 12).